Since the Paris Climate Agreement was adopted by consensus in December 2015, the global society has made various efforts to respond to this Agreement. The essential element of the Paris Climate Agreement is the so-called Nationally Determined Contributions (NDCs), specifying the long-term greenhouse gas (GHG) reduction targets beyond 2020. Unlike the different legal obligations of developed and developing countries specified in the precedent Kyoto Protocol, the NDCs under the Paris Climate Agreement apply equally to all countries. All the signed countries were asked to submit their Intended Nationally Determined Contributions (INDCs) before the 2015 Paris Climate Summit, which serve, unless otherwise provided, as the initial NDCs after the ratification of the Agreement. However, there is no mechanism to force a country to set a specific target by a specific date, but each target should go beyond previously set targets. Another challenge is that in June 2017, US President Donald Trump announced his intention to withdraw the US from the Agreement. Under the Agreement, the earliest effective date of withdrawal for the US is November 2020, shortly before the end of President Trump’s current term. The US was responsible for 15.5% of global CO2 emissions from fuel combustion in 2015 . The US’s withdrawal has brought a great uncertainty to the implementation of the Paris Climate Agreement and induced a lot of global disputes.